Though there are many analogies between time and space, there appear to be three commonplace yet deeply perplexing features of time that reveal it to be quite unlike space. These can be called ‘orientation’, ‘flow’ and ‘presence’. By orientation I mean that there is a direction to time, a temporal order between events which is not merely a reflection of how they are observed (what McTaggart 1908/1968 labelled the B-series time). Assertions that objects stand in spatial relations, such as to the left of, or above, or to the north of explicitly depend upon the position from which they are asserted or upon arbitrary, conventionally established spatial frameworks. There is nothing intrinsic about them; the objects involved are, so to speak, indifferent to them. Temporal relations are not like that – times are not just arranged along, as it were, a line but are successive along that imaginary line. Whether one event is before or after another is not (altogether) dependent upon how, or from where, they are viewed. Nature appears to respect temporal orientation, as enshrined in the laws of thermodynamics, though it remains a deep mystery exactly how the temporally symmetric basic laws of physics ground strongly asymmetric temporal processes (see Sklar 1993).